Multilevel waveguide structure

ABSTRACT

Integrated optical structures include a first wafer layer, a first insulator layer directly connected to the top of the first wafer layer, a second wafer layer directly connected to the top of the first insulator layer, a second insulator layer directly connected to the top of the second wafer layer, and a third wafer layer directly connected to the top of the second insulator layer. Such structures include: a first optical waveguide positioned within the second wafer layer; an optical coupler positioned within the second wafer layer, the second insulator layer, and the third wafer layer; and a second optical waveguide positioned within the third wafer layer. The optical coupler transmits an optical beam from the first optical waveguide to the second optical waveguide through the second insulator layer.

BACKGROUND

The present disclosure relates to optical waveguides, and morespecifically to optical waveguides in photonic integrated circuits.

A common wafer used in manufacturing integrated devices is an SOI(Silicon On Insulator) wafer. The SOI wafer has a silicon layer (SOIlayer) formed on a buried oxide (insulator) film, which is commonlyreferred to as the BOX layer. The SOI wafer has small parasiticcapacitance and high radiation resistance. The upper SOI layer, wheredevices are formed, is electrically and optically separated from thelower portion of the substrate by the BOX. Therefore, the SOI waferproduces high-speed and low-power consumption operation, prevents softerrors, and is regarded as a high-performance semiconductor device.

In many cases, the SOI wafers are produced by bonding methods, where asilicon oxide film is formed on the front surface of a silicon singlecrystal wafer, and then another silicon single crystal wafer is bondedto the oxide film on the first wafer. The bonding strength can beincreased by performing bonding heat treatment. Also, one of the wafers(e.g., the SOI layer) can be thinned by mirror polishing or ionimplantation to achieve desired performance and size considerations.Photonic integrated circuits (PIC) often form optical waveguides andother optical structures using the SOI layer.

SUMMARY

According to embodiments herein, some methods form an integrated opticalstructure by providing a first wafer layer that has a first wafer layertop. These methods form a first insulator layer on the first wafer layertop such that the first insulator layer bottom is directly connected tothe first wafer layer top, and the first insulator layer top is oppositethe first insulator layer bottom. Such methods bond a second wafer layerto the first insulator layer top, so that the second wafer layer bottomis directly connected to the first insulator layer top and the secondwafer layer top is opposite the second wafer layer bottom.

The methods then form a first optical waveguide within the second waferlayer. Also, these methods form a second insulator layer on the secondwafer layer top, so that the second insulator layer bottom is directlyconnected to the second wafer layer top and the second insulator layertop is opposite the second insulator layer bottom.

Further, such methods form an optical coupler within the secondinsulator layer, so that (in some embodiments) the second insulator isformed to be devoid of devices other than the optical coupler. Thesemethods bond a third wafer layer to the second insulator layer top suchthat the third wafer layer bottom is directly connected to the secondinsulator layer top and so that the third wafer layer top is oppositethe third wafer layer bottom. Furthermore, these methods form opticaland electrical devices on the third wafer layer.

The first wafer layer, first insulator layer, second wafer layer, secondinsulator layer and the third wafer layer, are planar layers that areformed to lie in different parallel planes. The optical coupler directsthe optical beam in a first direction perpendicular to the parallelplanes, and the optical coupler directs the optical beam in seconddirections parallel to the parallel planes. Thus, the optical coupler(positioned in the second insulator layer) transmits the optical beamfrom the first optical waveguide (that is in the second wafer layer) tothe second optical waveguide (that are in the third wafer layer) throughthe second insulator layer.

More specifically, the first optical waveguide is formed to have a firstoptical waveguide tapered end adjacent the optical coupler, similarlythe second optical waveguide is formed to have a second opticalwaveguide tapered end adjacent the optical coupler, and the opticalcoupler is formed to have corresponding optical coupler tapered endsadjacent the first optical waveguide tapered end and the second opticalwaveguide tapered end. The first optical waveguide tapered end is shapedto direct the optical beam from the first optical waveguide toward theoptical coupler in a direction parallel to the aforementioned parallelplanes; the optical coupler tapered ends are shaped to direct theoptical beam received from the first optical waveguide toward internalspaces of the optical coupler in a direction parallel to theaforementioned parallel planes, and to direct the optical beam from theinternal spaces of the optical coupler toward the second opticalwaveguide in a direction parallel to the aforementioned parallel planes;and the second optical waveguide tapered end is shaped to direct theoptical beam received from the optical coupler toward internal spaces ofthe second optical waveguide in a direction parallel to theaforementioned parallel planes.

Integrated optical structures herein include many components including afirst wafer layer that has a first wafer layer top. In these structures,a first insulator layer has a first insulator layer bottom that isdirectly connected to the first wafer layer top, and the first insulatorlayer has a first insulator layer top opposite the first insulator layerbottom.

Additionally, with these structures, a second wafer layer has a secondwafer layer bottom that is directly connected to the first insulatorlayer top, and the second wafer layer has a second wafer layer top thatis opposite the second wafer layer bottom. Also, a second insulatorlayer has a second insulator layer bottom that is directly connected tothe second wafer layer top, and the second insulator layer has a secondinsulator layer top that is opposite the second insulator layer bottom.Further, with such structures, a third wafer layer has a third waferlayer bottom that is directly connected to the second insulator layertop, and the third wafer layer has a third wafer layer top opposite thethird wafer layer bottom.

With such structures, a first optical waveguide is positioned within thesecond wafer layer; an optical coupler is positioned within the secondwafer layer, the second insulator layer, and the third wafer layer; andsecond optical waveguides and electrical devices are positioned in andon the third wafer layer. This optical coupler transmits an optical beamfrom the first optical waveguide to the second optical waveguide throughthe second insulator layer.

The first wafer layer, first insulator layer, second wafer layer, secondinsulator layer, and third wafer layer are planar layers which lie indifferent parallel planes. The optical coupler directs the optical beamin a first direction perpendicular to the parallel planes and theoptical coupler also directs the optical beam in second directionsparallel to the parallel planes.

More specifically, the first optical waveguide has a first opticalwaveguide tapered end adjacent the optical coupler, similarly the secondoptical waveguide has a second optical waveguide tapered end adjacentthe optical coupler, and the optical coupler has corresponding opticalcoupler tapered ends adjacent the first optical waveguide tapered endand the second optical waveguide tapered end. The first opticalwaveguide tapered end is shaped to direct the optical beam from thefirst optical waveguide toward the optical coupler in a directionparallel to the aforementioned parallel planes; the optical couplertapered ends are shaped to direct the optical beam received from thefirst optical waveguide toward internal spaces of the optical coupler ina direction parallel to the aforementioned parallel planes, and todirect the optical beam from the internal spaces of the optical couplertoward the second optical waveguide in a direction parallel to theaforementioned parallel planes; and the second optical waveguide taperedend is shaped to direct the optical beam received from the opticalcoupler toward internal spaces of the second optical waveguide in adirection parallel to the aforementioned parallel planes.

Other integrated optical structures herein include many componentsincluding a handle silicon wafer layer that has a handle silicon waferlayer top. In these structures, a first BOX layer has a first BOX layerbottom that is directly connected to the handle silicon wafer layer top,and the first BOX layer has a first BOX layer top opposite the first BOXlayer bottom.

Additionally, with these structures, a first SOI layer has a first SOIlayer bottom that is directly connected to the first BOX layer top, andthe first SOI layer has a first SOI layer top that is opposite the firstSOI layer bottom. Also, a second BOX layer has a second BOX layer bottomthat is directly connected to the first SOI layer top, and the secondBOX layer has a second BOX layer top that is opposite the second BOXlayer bottom. Further, with such structures, a second SOI layer has asecond SOI layer bottom that is directly connected to the second BOXlayer top, and the second SOI layer has a second SOI layer top oppositethe second SOI layer bottom.

With such structures, a first optical waveguide is positioned within thefirst SOI layer; an optical coupler is positioned within the first SOIlayer, the second BOX layer, and the second SOI layer; and secondoptical waveguides and electrical devices are positioned on the secondSOI layer. This optical coupler transmits an optical beam from the firstoptical waveguide to the second optical waveguide through the second BOXlayer.

The handle silicon wafer layer, first BOX layer, first SOI layer, secondBOX layer, and second SOI layer are planar layers which lie in differentparallel planes. The optical coupler directs the optical beam in a firstdirection perpendicular to the parallel planes and the optical coupleralso directs the optical beam in second directions parallel to theparallel planes.

More specifically, the first optical waveguide has a first opticalwaveguide tapered end adjacent the optical coupler, similarly the secondoptical waveguide has a second optical waveguide tapered end adjacentthe optical coupler, and the optical coupler has corresponding opticalcoupler tapered ends adjacent the first optical waveguide tapered endand the second optical waveguide tapered end. The first opticalwaveguide tapered end is shaped to direct the optical beam from thefirst optical waveguide toward the optical coupler in a directionparallel to the aforementioned parallel planes; the optical couplertapered ends are shaped to direct the optical beam received from thefirst optical waveguide toward internal spaces of the optical coupler ina direction parallel to the aforementioned parallel planes, and todirect the optical beam from the internal spaces of the optical couplertoward the second optical waveguide in a direction parallel to theaforementioned parallel planes; and the second optical waveguide taperedend is shaped to direct the optical beam received from the opticalcoupler toward internal spaces of the second optical waveguide in adirection parallel to the aforementioned parallel planes.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will be better understood from the followingdetailed description with reference to the drawings, which are notnecessarily drawn to scale and in which:

FIG. 1 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 2 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 3 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 4 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 5 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 6 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 7 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 8 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 9 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 10 is a side-view schematic diagram illustrating partially formedstructures herein;

FIG. 11 is a side-view schematic diagram illustrating structures herein;

FIG. 12 is a top-view schematic diagram illustrating structures herein;

FIG. 13 is a perspective-view schematic diagram illustrating structuresherein;

FIG. 14A is a top-view schematic diagram illustrating structures herein;

FIG. 14B is a side-view schematic diagram of FIG. 14A illustratingstructures herein;

FIG. 15A is a top-view schematic diagram illustrating structures herein;

FIG. 15B is a side-view schematic diagram view along line B-B in FIG.15A illustrating structures herein;

FIG. 15C is a side-view schematic diagram view along line C-C in FIG.15A illustrating structures herein; and

FIG. 16 is a flow diagram illustrating embodiments herein.

DETAILED DESCRIPTION

According to embodiments herein, methods herein form an integratedoptical structure. As shown in FIG. 1, which is a side-view schematicdiagram, such methods provide a first wafer layer (e.g., uniformsingle-crystal orientation silicon wafer layer, which is sometimesreferred to as a “handle” wafer) 102.

As shown in FIG. 2, these methods form a first insulator layer (e.g., afirst buried oxide (BOX) layer) 104 on the arbitrarily named “top” ofthe first wafer layer 102 such that the “bottom” of the first insulatorlayer 104 is directly connected to the top of the first wafer layer 102.As in all structures herein, the arbitrarily named “top” of the firstinsulator layer 104 is opposite the arbitrarily named “bottom” of thefirst insulator layer 104, and the terms “top” and “bottom” herein arenot intended to require any specific orientation, but are merely used asshorthand terms to more easily identify different sides of structuresthat relatively oppose one another.

The insulator layers herein can be formed by growth or depositionprocesses, as is understood by those ordinarily skilled in the art. Insome examples, the dielectrics (insulators) mentioned herein can, forexample, be grown from either a dry oxygen ambient or steam, etc.Alternatively, the insulators herein may be formed from any of the manycandidate high dielectric constant (high-k) materials, including but notlimited to silicon nitride, silicon oxynitride, of SiO₂ and Si₃N₄, metaloxides such as tantalum oxide, etc. The thickness of dielectrics hereinmay vary contingent upon the required device performance and size;however, the BOX layers herein are sufficiently thick to form aneffective optical insulator (opaque light blocking layer, and aregenerally 2 um or more thick for optical isolation).

FIG. 3 illustrates that such methods bond a second wafer layer (e.g.,first silicon-on-insulator (SOI) layer) 106 to the top of the firstinsulator layer 104, so that the bottom of the second wafer layer 106 isdirectly connected to the top of the first insulator layer 104 and thetop of the second wafer layer 106 is opposite the bottom of the secondwafer layer 106. The bonding processes used herein can include anyattachment process presently known or developed in the future, and caninclude heating processes, using chemical adhesives, etc., as isunderstood by those ordinarily skilled in the art. If desired, thethickness of any layer herein can be reduced by any known or newlydeveloped etching or polishing processes, as shown with the thinnedwafer layers 106 and 110 in FIGS. 5 and 8 discussed in detail below.

The methods then pattern openings 122, as shown in FIG. 4. While notillustrated to keep the drawings succinct, when patterning any materialherein, a patterning layer (such as an organic photoresist) can beformed over the material to be patterned. The patterning layer (resist)can be exposed to some pattern of light radiation (e.g., patternedexposure, laser exposure, etc.) provided in a light exposure pattern,and then the resist is developed using a chemical agent. This processchanges the physical characteristics of the portion of the resist thatwas exposed to the light. Then one portion of the resist can be rinsedoff, leaving the other portion of the resist to act as a mask to protectthe material to be patterned (which portion of the resist that is rinsedoff depends upon whether the resist is a positive resist (illuminatedportions remain) or negative resist (illuminated portions are rinsedoff)). A material removal process is then performed (e.g., plasmaetching, etc.) to remove the unprotected portions of the material belowthe resist to be patterned. The resist is subsequently removed to leavethe underlying material patterned according to the light exposurepattern (or a negative image thereof).

As shown in FIG. 5, an insulator (e.g., oxide) 124 and a claddingmaterial 128 are grown or deposited in the openings 122 to form anoptical waveguide 130 between the cladding material 128 (as separated bythe insulator 124, which can be for example, 10 nm to 200 nm thick)within the second wafer layer 106. The characteristics of all of thecladding material, cooperate with the unaltered SOI wafer 106 so thatlight remains predominantly inside the waveguide 130. The claddingmaterials can be any known or later developed cladding materialsincluding, for example, an oxide (such as silicon dioxide), a nitride(such as silicon nitride, where the substrate is silicon-based). Also,the cladding material can be a polymer, silicon oxynitride, sapphire, aIII-V compound semiconductor, a chalcogenide, etc. While only a singlewaveguide 130 is shown in FIG. 5, as is understood by those ordinarilyskilled in the art, SOI wafer 106 can include multiple waveguides, asshown in FIGS. 15A-15C, discussed below.

Also, as shown in FIG. 6, these methods form a second insulator layer(second BOX layer) 108 on the top of the second wafer layer 106, so thatthe bottom of the second insulator layer 108 is directly connected tothe top of the second wafer layer 106 (using any of the processesdiscussed above). Again, the “top” of the second insulator layer 108 isopposite the “bottom” of the second insulator layer 108.

Further, as shown in FIG. 7, these methods bond a third wafer layer(e.g., second SOI layer) 110 to the top of the second insulator layer108 such that the bottom of the third wafer layer 110 is directlyconnected to the top of the second insulator layer 108 and so that thetop of the third wafer layer 110 is opposite the bottom of the thirdwafer layer 110.

As with wafer layer 106, wafer layer 110 can be similarly thinned, usingthe processing discussed above, as shown in FIG. 8. As also shown inFIG. 8, such methods pattern additional openings 126 (using theprocessing discussed above) into and/or through the third wafer layer110, the second insulator layer 108, and the second wafer layer 106, andform insulators 124.

As shown in FIG. 9, the methods herein form, deposit, or insert apreviously created optical coupler 132 within one of the openings 126.Further, using similar processing to that discussed above, the methodsherein grow or deposit cladding material 128 in one of the openings 126to define an optical waveguide 136 between the cladding material 128 andthe optical coupler 132 within the third wafer layer 110. Again, thecharacteristics of the cladding material 128 cooperates with theunaltered SOI wafer 110 so that light remains predominantly inside thewaveguide 136. While only a single optical coupler 132 is shown in FIG.9, as is understood by those ordinarily skilled in the art, thesestructures can include multiple optical couplers 132, as shown in FIGS.15A-15C, discussed below.

To form any optical coupler 132 herein, a material capable oftransmitting light is formed in any previously formed opening (or theoptical device is manufactured separately and attached to any of thelayers of the structure) and the surrounding layer acts as areflector/refractor to keep the light within the optical coupler 132.Some exemplary materials that can be used to form optical couplingdevices herein include the SOI layer itself, silica (SiO₂) on silicon,various polymers and compound semiconductor materials such as GaAs, InP,and GaN, monocrystalline silicon, polycrystalline silicon, amorphoussilicon (a-Si), silicon nitride (SiN_(x)), e.g., Si₃N₄, silicon oxynitride (SiON), germanium, III-V compound semiconductors, II-VI compoundsemiconductors, IV-VI compound semiconductors, a chalcogenide such asarsenic selenide (As₂Se₃) or arsenic sulphide (As₂S₃) and germaniumantimony sulphide (GeSbS), etc. These materials are generally capable oftransmitting optical beams having wavelengths ranging from theUV/visible spectrum (200-750 nm) to near Infrared spectrum (750 nm-1650nm).

As shown in FIGS. 4 and 8, the various openings 122 and 126 arepatterned to position the waveguides 130 and 132, and the opticalcoupler 132 directly next to one another (without any interveningmaterials other than the insulators 124) to allow each device totransmit and receive light to and from the other. Further, the opticalcoupler 132 is formed to extend through the second wafer layer 106, thesecond insulator layer 108, and the third wafer layer 110 to transmitlight between the different waveguides 130 and 136 (where light waves(or light beams) are shown with white arrow 160 in the drawings).

Furthermore, as shown in FIG. 10, these methods form optical devices 140in the third wafer layer 110 (through growth, deposition, attachment ofpreviously manufactured optical devices, etc. (and the details of theformation of such devices are not illustrated for conciseness)).Similarly, as shown in FIG. 11, electrical devices 150, 152 are formedon and/or in the top of the third wafer layer 110 (through growth,deposition, attachment of previously manufactured optical devices, etc.(and again the details of the formation of such devices are notillustrated for conciseness)).

As is understood by those ordinarily skilled in the art, such opticaldevices 140 can include, but are not limited to passive devices (such asoptical beam splitters, optical wavelength filters, optical resonators,optical waveguides, optical wavelength multiplexers, optical couplers,optical polarizers, optical isolators, polarization rotators, etc.),emissive devices (such as optical amplifiers, lasers, light-emittingdevices, etc.), absorptive devices (such as photodetectors, etc.),electro-optic devices (such as electro-optic modulators, electro-opticphase shifters, electro-optic switches, etc.), and nonlinear-opticaldevices (such as second harmonic generators, photonic transistor, andall-optical switches etc.). Similarly, such electronic devices 150, 152can include, but are not limited to conductors, insulators, transistors,diodes, resistors, capacitors, inductors, etc. Methods for manufacturingsuch devices are well known to those ordinarily skilled in the art, andare not discussed in detail herein to keep focus on the salient featuresof the disclosed structures and methods herein.

Generally, transistor structures (e.g., 150, 152) are formed bydepositing or implanting impurities into a substrate to form at leastone semiconductor channel region, bordered by shallow trench isolationregions below the top (upper) surface of the substrate. A “substrate” orwafer herein can comprise any material appropriate for the given purpose(whether now known or developed in the future) and can comprise, forexample, Si, SiC, SiGe, SiGeC, other III-V or II-VI compoundsemiconductors, or organic semiconductor structures, etc. The “shallowtrench isolation” (STI) structures are well-known to those ordinarilyskilled in the art and are generally formed by patterningopenings/trenches within the substrate and growing or filling theopenings with a highly insulating material (this allows different activeareas of the substrate to be electrically isolated from one another).

As also shown in FIG. 11, the first wafer layer 102, first insulatorlayer 104, second wafer layer 106, second insulator layer 108 and thethird wafer layer 110, are planar layers that are formed to lie indifferent parallel planes. The optical coupler 132 directs the opticalbeam in a first direction perpendicular to the parallel planes, and theoptical coupler 132 directs the optical beam in second directionsparallel to the parallel planes (see the discussion of FIGS. 14A-14Bbelow). Thus, the optical coupler 132 (positioned in the second waferlayer 106, second insulator layer 108, and the third wafer layer 110)and the second waveguide 136 transmit the optical beam from the opticalwaveguide 130 (that is in the second wafer layer 106) to the opticaldevices 140 (that are in the third wafer layer 110) through the secondinsulator layer 108 and the third wafer layer 110.

Thus, as shown in FIG. 11, integrated optical structures herein includemany components including a handle silicon wafer layer 102. In thesestructures, a first BOX layer 104 has a bottom that is directlyconnected to the top of the handle silicon wafer layer 102, and thefirst BOX layer 104 has a top opposite the bottom of the first BOX layer104 bottom. Additionally, with these structures, a first SOI layer 106has a bottom that is directly connected to the top of the first BOXlayer 104, and the first SOI layer 106 has a top that is opposite thebottom of the first SOI layer 106. Also, a second BOX layer 108 has abottom that is directly connected to the top of the first SOI layer 106,and the second BOX layer 108 has a top that is opposite the bottom ofthe second BOX layer 108. Further, with such structures, a second SOIlayer 110 has a bottom that is directly connected to the top of thesecond BOX layer 108, and the second SOI layer 110 has a top oppositethe bottom of the second SOI layer 110.

With such structures, a first optical waveguide 130 is positioned withinthe first SOI layer 106; an optical coupler 132 is positioned within thefirst SOI layer 106, the second BOX layer 108, and the second SOI layer110; a second optical waveguide 136 is positioned within the second SOIlayer 110; and optical devices 140 and electrical devices 150, 152 arepositioned in and on the second SOI layer 110. This optical coupler 132transmits an optical beam from the optical waveguide 130 to the secondoptical waveguide 136 through the second BOX layer 108.

As shown in FIG. 11, the handle silicon wafer layer 102, first BOX layer104, first SOI layer 106, second BOX layer 108, and second SOI layer 110are planar layers that lie in different parallel planes. The opticalcoupler 132 directs the optical beam in a first direction perpendicularto the parallel planes and the optical coupler 132 also directs theoptical beam in second directions parallel to the parallel planes.Additionally, the handle silicon wafer 102 is devoid of any devices, andthe handle silicon wafer 102 consists of only single-crystal silicon.

FIG. 12 is a top-view schematic diagram and FIG. 13 is aperspective-view schematic diagram, both illustrating structures hereinand such figures illustrate that the optical coupler 132 can be avertical ring coupler positioned within the first SOI layer 106, thesecond BOX layer 108, and the second SOI layer 110. The optical signal(or light) can be moved from buried waveguide 130 to top silicon layer110 and vice-versa using vertical ring couplers 132. In FIG. 12, thedash lines represent the buried waveguides 130. Items 132 are the ringcouplers in space from the bottom to top silicon layers, though the topBOX. The solid lines (items 136) represent devices or waveguides in thetop silicon layer 110.

FIG. 14A is a top-view schematic diagram and FIG. 14B is a side-viewschematic diagram, both illustrating the optical coupler in the form ofa uniquely designed vertical adiabatic coupler 132. The white line (item160) in FIGS. 14A-14B depicts the light path through the device from top110 to bottom 102, or vice versa.

As noted above, the handle silicon wafer layer 102, first BOX layer 104,first SOI layer 106, second BOX layer 108, and second SOI layer 110 areplanar layers which lie in different parallel planes, and as shown inFIGS. 14A-14B, the optical coupler 132 directs the optical beam in afirst direction perpendicular to the parallel planes and the opticalcoupler 132 also directs the optical beam in second directions parallelto the parallel planes. In other words, the optical coupler shown inFIGS. 14A-14B directs the light beam in two different directions thatare perpendicular to one another and therefore transmits the light beamboth up through the device, and across the device.

More specifically, in FIGS. 14A-14B the first optical waveguide 130 isformed to have a first optical waveguide tapered end 138 adjacent theoptical coupler 132. Similarly the second optical waveguide 136 isformed to have a second optical waveguide tapered end 144 adjacent theoptical coupler 132. The optical coupler 132 is formed to havecorresponding optical coupler tapered ends 134, one of which is adjacentthe first optical waveguide tapered end 138 and the other of which isadjacent the other second optical waveguide tapered end 144. The tapersdiscussed herein can have any useful angle with respect to the parallelplanes discussed herein (or with respect to perpendicular to suchparallel planes), such as 25°, 30°, 45°, 60°, 80°, etc.; and while onetaper angle is shown in FIGS. 14A-14B, those ordinarily skilled in theart would understand that different angles would be used withdifferently spaced structures, different light wavelengths, differentoptic materials, etc.

The various openings described above are patterned into shapes so thatthe waveguide 130, the optical coupler 132, and the optical devices 140have the shapes shown in FIGS. 14A-14B. Therefore, for example, openings122 shown in FIG. 4 are shaped (patterned) so that the first opticalwaveguide tapered end 138 is shaped to direct (and receive) the opticalbeam from the optical waveguide 130 toward one of the optical couplertapered ends 134 in a direction parallel to the aforementioned parallelplanes, as shown in FIGS. 14A-14B. Similarly, the openings 126 shown inFIG. 8 are shaped (patterned) so that the optical coupler tapered ends134 are shaped as shown in FIGS. 14A-14B.

Thus, the optical coupler tapered ends 134 are shaped to direct (andreceive) the optical beam received from the optical waveguide 130 towardinternal spaces of the optical coupler 132 (in a direction parallel tothe aforementioned parallel planes, as shown by light beam path 160).Further, the optical coupler tapered ends 134 are shaped to direct (andreceive) the optical beam from the internal spaces of the opticalcoupler 132 toward the optical waveguide 136 (in a direction parallel tothe aforementioned parallel planes, as shown by light beam path 160).Correspondingly, when formed in FIG. 9, the second optical waveguidetapered end 144 is shaped to direct (and receive) the optical beamreceived from the optical coupler 132 toward internal spaces of theoptical waveguide 136 (in a direction parallel to the aforementionedparallel planes, as shown by light beam path 160). As is understood bythose ordinarily skilled in the art, reflection and refraction cause thelight beam to be transmitted through such structures.

FIG. 15A is a top-view schematic diagram, FIG. 15B is a side-viewschematic diagram view along line B-B in FIG. 15A, and FIG. 15C is aside-view schematic diagram view along line C-C in FIG. 15A illustratingthe positioning of the waveguides 130, the optical couplers 132, and theoptical waveguide 136 showing one exemplary arrangement of the devicesthat are discussed above.

Therefore, the optical coupler 132 can be a ring coupler (FIGS. 12-13)or a vertical adiabatic coupler (FIGS. 14A-15C). While the ring coupleris limited to a single wavelength of light, the vertical adiabaticcoupler can handle a wide range of wavelengths.

Thus, the structures and methods presented above use a double BOX SOIwafer with embedded waveguides and vertical couplers to transfer opticalsignal to different silicon levels, which saves area on the chip andimproves optical coupling between the fiber-optic cable and chip.

More specifically, the first waveguide 130 in the first SOI layer 106does not consume any of the scarce area of the second SOI layer 110,allowing the relatively scarce area of the second SOI layer 110 to beused for electronic and optical devices. Note that the second waveguide136 is included within the second SOI layer 110; however, the secondwaveguide 136 can be substantially shorter than the first waveguide 130,thereby freeing up a large amount of the area of the second SOI layer110. For example, as shown in FIGS. 12 and 13, the second waveguide 136can extend from the optical coupler 132 (a ring coupler in this example)for a distance that is limited to only the length of the differentoptical devices that are to be supplied with the optical beam from thatoptical coupler 132. To the contrary, the first waveguide 130 can have amuch greater length (e.g., 5×, 10×, 50×, 100×, 1000×, etc.) relative tothe length of the second waveguide 136, and the first waveguide 130 mayrun from the connection to the fiber optic cable to the optical coupler132.

Thus, in one extreme example, the first waveguide 132 may be as long asthe full width of the chip, while the second waveguide 136 may only beas long as a single optical device located on the chip. Having only thesmaller second waveguides 136 on the second SOI layer 110 frees up asubstantial amount of area on the second SOI layer 110. Additionally, insome examples, the first waveguide 130 may be connected to many opticalcouplers 132, and may supply the optical beam to multiple secondwaveguides 136.

Additionally, since the only devices that are positioned within thefirst SOI layer 106 are the optical coupler 132, the cladding areas 128,and the first optical waveguides 130; it is much easier to route thefirst optical waveguides 130 (because they do not need to be routedaround various electrical and optical devices (140, 142, 150, 152) thatwill be included within the second SOI layer 110). Additionally, asshown above, the first SOI layer 106 is bounded by relatively thickerinsulator layers 104, 108, which allows the first optical waveguides 130to experience much less noise and optical loss, relative to what thefirst optical waveguides 130 would experience if they were locatedwithin the second SOI layer 110. Also, as shown in FIG. 11, thesestructure and methods provide better coupling to, and make more siliconarea available to the outside fiber (allowing an easier connection tothe relatively large fiber-optic cable, because such connections arespaced from the second SOI layer 110).

FIG. 16 is a flow diagram illustrating various methods herein. Theseexemplary methods form an integrated optical structure by firstproviding a first wafer layer that has a first wafer layer top in item200. These methods then form a first insulator layer on the first waferlayer top (item 202) such that the first insulator layer bottom isdirectly connected to the first wafer layer top, and the first insulatorlayer top is opposite the first insulator layer bottom. Such methodsalso bond a second wafer layer to the first insulator layer top (item204), so that the second wafer layer bottom is directly connected to thefirst insulator layer top and the second wafer layer top is opposite thesecond wafer layer bottom.

The methods then form a first optical waveguide within the second waferlayer (item 206). Also, in item 208, these methods form a secondinsulator layer on the second wafer layer top, so that the secondinsulator layer bottom is directly connected to the second wafer layertop and the second insulator layer top is opposite the second insulatorlayer bottom.

As shown in item 210, these methods bond a third wafer layer to thesecond insulator layer top such that the third wafer layer bottom isdirectly connected to the second insulator layer top and so that thethird wafer layer top is opposite the third wafer layer bottom. Further,such methods form an optical coupler within the second insulator layer(item 212, so that (in some embodiments) the second insulator is formedto be devoid of devices other than the optical coupler. In item 214,such methods form the second optical waveguide within the third waferlayer. Furthermore, in item 216, these methods form optical andelectrical devices on the third wafer layer.

The first wafer layer, first insulator layer, second wafer layer, secondinsulator layer and the third wafer layer, are planar layers that areformed to lie in different parallel planes. The optical coupler formedin item 210 directs the optical beam in a first direction perpendicularto the parallel planes, and the optical coupler directs the optical beamin second directions parallel to the parallel planes. Thus, the opticalcoupler (positioned in the second insulator layer) transmits the opticalbeam from the optical waveguide (that is in the second wafer layer) tothe optical devices (that are on the third wafer layer) through thesecond insulator layer.

More specifically, the first optical waveguide is formed in item 206 tohave a first optical waveguide tapered end adjacent the optical coupler,similarly the second optical waveguide is formed in item 214 to have asecond optical waveguide tapered end adjacent the optical coupler, andthe optical coupler is formed in item 210 to have corresponding opticalcoupler tapered ends adjacent the first optical waveguide tapered endand the second optical waveguide tapered end. The first opticalwaveguide tapered end is shaped to direct the optical beam from theoptical waveguide toward the optical coupler in a direction parallel tothe aforementioned parallel planes; the optical coupler tapered ends areshaped to direct the optical beam received from the optical waveguidetoward internal spaces of the optical coupler in a direction parallel tothe aforementioned parallel planes, and to direct the optical beam fromthe internal spaces of the optical coupler toward the optical device ina direction parallel to the aforementioned parallel planes; and thesecond optical waveguide tapered end is shaped to direct the opticalbeam received from the optical coupler toward internal spaces of theoptical device in a direction parallel to the aforementioned parallelplanes.

These methods also form a connection to a fiber-optic cable, as shown initem 218. While this connection can be formed at any step in theprocess, it is arbitrarily shown in FIG. 16 as item 218. The fiber-opticcable transmits the optical beam to the optical waveguide that ispositioned in the second wafer layer; however, the optical device on thethird wafer layer only receives the optical beam through the opticalcoupler, and does not directly receive the optical beam from thefiber-optic cable.

The method as described above is used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

While only one or a limited number of devices are illustrated in thedrawings, those ordinarily skilled in the art would understand that manydifferent types similar devices could be simultaneously formed with theembodiment herein and the drawings are intended to show simultaneousformation of multiple different types of such devices; however, thedrawings have been simplified to only show a limited number of devicesfor clarity and to allow the reader to more easily recognize thedifferent features illustrated. This is not intended to limit thisdisclosure because, as would be understood by those ordinarily skilledin the art, this disclosure is applicable to all such similarstructures.

In addition, terms such as “right”, “left”, “vertical”, “horizontal”,“top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”,“over”, “overlying”, “parallel”, “perpendicular”, etc., used herein areunderstood to be relative locations as they are oriented and illustratedin the drawings (unless otherwise indicated). Terms such as “touching”,“on”, “in direct contact”, “abutting”, “directly adjacent to”, etc.,mean that at least one element physically contacts another element(without other elements separating the described elements).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of this disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. An integrated optical structure comprising: afirst wafer layer having a first wafer layer top; a first insulatorlayer having a first insulator layer bottom directly connected to saidfirst wafer layer top, and having a first insulator layer top oppositesaid first insulator layer bottom; a second wafer layer having a secondwafer layer bottom directly connected to said first insulator layer top,and having a second wafer layer top opposite said second wafer layerbottom; a second insulator layer having a second insulator layer bottomdirectly connected to said second wafer layer top, and having a secondinsulator layer top opposite said second insulator layer bottom; a thirdwafer layer having a third wafer layer bottom directly connected to saidsecond insulator layer top, and having a third wafer layer top oppositesaid third wafer layer bottom; a first optical waveguide positionedwithin said second wafer layer; a second optical waveguide positionedwithin said third wafer layer; an optical coupler on said firstinsulator layer and extending vertically through said second wafer layerso as to be positioned laterally adjacent to said first opticalwaveguide, through said second insulator layer, and through said thirdwafer layer so as to be positioned laterally adjacent to said secondoptical waveguide; and insulators within said second wafer layer andsaid third wafer layer, said insulators separating said first opticalwaveguide from said optical coupler within said second wafer layer andseparating said second optical waveguide from said optical coupler insaid third wafer layer, said optical coupler transmitting an opticalbeam from said first optical waveguide to said second optical waveguidethrough said second insulator layer.
 2. The integrated optical structureaccording to claim 1, said first optical waveguide comprising a firstoptical waveguide tapered end adjacent said optical coupler, said secondoptical waveguide comprising a second optical waveguide tapered endadjacent said optical coupler, said optical coupler comprising opticalcoupler tapered ends adjacent said first optical waveguide tapered endand said second optical waveguide tapered end, said first opticalwaveguide tapered end being shaped to direct said optical beam from saidfirst optical waveguide toward said optical coupler, said opticalcoupler tapered ends being shaped to direct said optical beam receivedfrom said first optical waveguide toward internal spaces of said opticalcoupler, and to direct said optical beam from said internal spaces ofsaid optical coupler toward said second optical waveguide, and saidsecond optical waveguide tapered end being shaped to direct said opticalbeam received from said optical coupler toward internal spaces of saidsecond optical waveguide.
 3. The integrated optical structure accordingto claim 2, said first wafer layer, said first insulator layer, saidsecond wafer layer, said second insulator layer, and said third waferlayer comprising planar layers lying in different, parallel planes, saidoptical coupler directing said optical beam in a first directionperpendicular to said parallel planes, and said optical coupler taperedends directing said optical beam in second directions parallel to saidparallel planes.
 4. The integrated optical structure according to claim1, said optical coupler comprising a ring coupler.
 5. The integratedoptical structure according to claim 1, said second insulator layerbeing devoid of devices other than said optical coupler.
 6. Theintegrated optical structure according to claim 1, further comprisingelectrical devices positioned on said third wafer layer top.
 7. Theintegrated optical structure according to claim 1, said first waferlayer being devoid of any devices, and said first wafer layer consistingof only single-crystal silicon.
 8. An integrated optical structurecomprising: a first wafer layer having a first wafer layer top; a firstinsulator layer having a first insulator layer bottom directly connectedto said first wafer layer top, and having a first insulator layer topopposite said first insulator layer bottom; a second wafer layer havinga second wafer layer bottom directly connected to said first insulatorlayer top, and having a second wafer layer top opposite said secondwafer layer bottom; a second insulator layer having a second insulatorlayer bottom directly connected to said second wafer layer top, andhaving a second insulator layer top opposite said second insulator layerbottom; a third wafer layer having a third wafer layer bottom directlyconnected to said second insulator layer top, and having a third waferlayer top opposite said third wafer layer bottom; a first opticalwaveguide positioned within said second wafer layer; a second opticalwaveguide positioned within said third wafer layer; and an opticalcoupler positioned within said second wafer layer, said second insulatorlayer, and said third wafer layer, said optical coupler transmitting anoptical beam from said first optical waveguide to said second opticalwaveguide through said second insulator layer, said first opticalwaveguide comprising a first optical waveguide tapered end adjacent saidoptical coupler, said second optical waveguide comprising a secondoptical waveguide tapered end adjacent said optical coupler, saidoptical coupler comprising optical coupler tapered ends adjacent saidfirst optical waveguide tapered end and said second optical waveguidetapered end, said first optical waveguide tapered end being shaped todirect said optical beam from said first optical waveguide toward saidoptical coupler, said optical coupler tapered ends being shaped todirect said optical beam received from said first optical waveguidetoward internal spaces of said optical coupler, and to direct saidoptical beam from said internal spaces of said optical coupler towardsaid second optical waveguide, and said second optical waveguide taperedend being shaped to direct said optical beam received from said opticalcoupler toward internal spaces of said second optical waveguide.
 9. Theintegrated optical structure according to claim 8, said first waferlayer, said first insulator layer, said second wafer layer, said secondinsulator layer, and said third wafer layer comprising planar layerslying in different, parallel planes, said optical coupler directing saidoptical beam in a first direction perpendicular to said parallel planes,and said optical coupler tapered ends directing said optical beam insecond directions parallel to said parallel planes.
 10. The integratedoptical structure according to claim 8, said optical coupler comprisinga ring coupler.
 11. The integrated optical structure according to claim8, said second insulator layer being devoid of devices other than saidoptical coupler.
 12. The integrated optical structure according to claim8, further comprising electrical devices positioned on said third waferlayer top.
 13. The integrated optical structure according to claim 8,said first wafer layer being devoid of any devices, and said first waferlayer consisting of only single-crystal silicon.